Non-invasive intracranial pressure monitoring system and method thereof

ABSTRACT

A system which includes a first sensor placed proximate to a perfusion field of an artery receiving blood which emanates from the cranial cavity is configured to monitor pulsations of the artery receiving blood which emanates from the cranial cavity artery. A second sensor placed proximate to a perfusion field of an artery which does not receive blood emanating from the cranial cavity configured to monitor pulsations of the artery which does not receive blood emanating from the cranial cavity. A third sensor configured to monitor pulsations of a distal artery. A processing system responsive to signals from the first, second, and third sensors is configured to determine intracranial pressure.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/551,127, filed on Nov. 24, 2014, and claims the benefit of andpriority thereto under 35 U.S.C. §§ 119, 120, 363, 365, and 37 C.F.R. §1.55 and § 1.78, which is incorporated herein by this reference, andpatent application Ser. No. 14/551,127, filed on Nov. 24, 2014 is acontinuation of U.S. patent application Ser. No. 13/939,824 (now U.S.Pat. No. 9,862,913), filed on Nov. 7, 2013, which claims the benefit ofand priority thereto under 35 U.S.C. §§ 119, 120, 363, 365, and 37C.F.R. § 1.55 and § 1.78, which is also incorporated herein byreference.

GOVERNMENT RIGHTS

This invention was made with U.S. Government support under Contract No.N68335-10-C-0079, awarded by the U.S. Navy, and W81XWH-09-C-0118,awarded by the U.S. Army. The Government has certain rights in theinvention.

FIELD OF THE INVENTION

This invention relates to a non-invasive intracranial pressuremonitoring system and method thereof.

BACKGROUND OF THE INVENTION

A closed-head brain injury, whether incurred as a result of blunt forcetrauma or a blast wave, can have insidious effects on a person. Althoughmany casualties may suffer from headache or dizziness, it is difficultwith conventional systems and methods to image every soldier or athletein the field who experiences a potential brain injury. Most conventionalimaging methods are large and require significant power. Moreover,damage to delicate brain tissues is frequently undetectable byconventional imaging, including CT scanning, even when such imaging isavailable.

The brain, however, is a soft organ with delicate structures held withina fixed volume. Damage to the small structures within a brain causelocal swelling and cerebral blood flow and systemic blood pressure maynot necessarily decrease with brain swelling. Therefore, even mildswelling of about 1 to 3 cc of extra fluid results in increasedpressure. This elevated intracranial pressure (ICP) can itself causemore damage, including brain cell death and permanent brain injury ordeath.

In many active populations, especially true of the armed forces, orprofessional sports, a casualty may try to shrug off the seemingly mildsymptoms of headache, dizziness, and the like. However, an unknownpercentage of these injured are experiencing clinically significantelevated ICP which may worsen or result in permanent damage which couldotherwise be avoided with the appropriate application of pharmacologicalor surgical interventions.

Currently, there is no known robust, portable, and reliable system ormethod which can accurately monitor ICP without direct access to theintracranial space. Therefore, it may not be feasible to check ICP onevery person who has or may have experienced trauma to the brain. It isunknown how many casualties of blunt or blast trauma have underlyingincreased pressure in the brain that occurs in response to the injury.

The best conventional systems currently available to identify whichcasualties are at the most risk of brain injury are those that monitorthe physical trauma (such as blast waves or impact) the headexperiences. However, such conventional systems may only provideinformation based on an empirical diagnostic technique which may nottake into account individual variability with regards to susceptibilityof brain injury. Thus, two people experiencing the same physical traumaare likely to exhibit different levels of damage, but without a directmeasure of the damage, they may be impossible to differentiate.

There are many conventional systems and methods that may hold promisefor being able to measure or monitor ICP without direct access to thebrain. These conventional systems and methods often employ large, heavy,power intensive equipment, such as MRI, and the like, and therefore arenot portable. This limits their use in the battlefield or at thesidelines in sports related injuries.

The supraorbital artery provides an avenue of information from thecranial cavity. This vessel emanates from the internal carotid arteryvia the orbit and is readily accessible at the forehead. By virtue ofits path along the periphery of the brain, it carries with itinformation related to the ICP. U.S. Pub. No. 2009/0143656 to Manwaringet al., discloses that the supraorbital artery may be used to determineICP. However, as disclosed therein, only two sensors are used which maylimit the accuracy of the measured ICP. Moreover, to date no practicaldevice has emerged from the '656 patent application.

Thus, there is a need for a system and method that can measure ICPnoninvasively, unobtrusively and continuously to provide an accuratemeasure of the extent of brain injury and enable medical care to timelyprovide the needed care. Moreover, in cases where the injury might havegone undetected until extensive damage has been done due to uncheckedswelling, there is a need for effective threat agent that more quicklyresolves the problem and returns the injured person to work, a soldierto duty, or an athlete to top performance.

SUMMARY OF THE INVENTION

In one aspect, a non-invasive intracranial pressure monitoring system isfeatured. A first sensor placed proximate to a perfusion field of anartery receiving blood which emanates from the cranial cavity isconfigured to monitor pulsations of the artery receiving blood whichemanates from the cranial cavity artery. A second sensor is placedproximate to a perfusion field of an artery which does not receive bloodemanating from the cranial cavity configured to monitor pulsations ofthe artery which does not receive blood emanating from the cranialcavity. A third sensor is configured to monitor pulsations of a distalartery. A processing system responsive to signals from the first,second, and third sensors is configured to determine intracranialpressure.

In one embodiment, the first sensor may be placed on the forehead. Thesecond sensor may be placed on or near the temple on or near the ear.The third sensor may be placed distally on a finger, on a hand, or on aforearm. The processing subsystem may be configured to determine theintracranial pressure by correlating signals from the first sensor tosignals from the third sensor and correlating signals from the secondsensor to signals from the third sensor and combining the determinedcorrelations. The processing subsystem may be configured to determinethe intracranial pressure by determining the magnitude and phase of thespectral components of signals from each of the first, second, and thirdsensors and comparing the magnitude or the phase of the spectralcomponents of the first sensor to the magnitude or the phase of thespectral components of third sensor and the magnitude or the phase ofthe spectral components of the second sensor to the magnitude or thephase components of the third sensor and combining the compared values.The processing subsystem may be configured to adjust the value of thecomponent phases according to differences in magnitudes of associatedspectral components. The processing subsystem may be configured todetermine the intracranial pressure by combining the signals from thefirst sensor with the signals from the second sensor and combining theresult with the signals from the third sensor. The system may include adisplay coupled to the processing subsystem configured to display theintracranial pressure.

In another aspect, a non-invasive intracranial pressure monitoringsystem is featured. A first sensor placed proximate to the supraorbitalartery is configured to monitor pulsations of the supraorbital artery. Asecond sensor placed proximate to a branch of the external carotidartery is configured to monitor pulsations of the external carotidartery. A third sensor is configured to monitor pulsations of a distalartery. A processing subsystem responsive to signals from the first,second, and third sensors is configured to determine intracranialpressure.

In another embodiment, the first sensor may be placed on the forehead.The second sensor may be placed on or near the temple, or near the ear.The third sensor may be placed distally on a finger, or on a hand, or aforearm. The processing subsystem may be configured to determine theintracranial pressure by correlating signals from the first sensor tosignals from the third sensor and correlating signals from the secondsensor to signals from the third sensor and combining the determinedcorrelations. The processing subsystem may be configured to determinethe intracranial pressure by determining the magnitude and phase of thespectral components of signals from each of the first, second, and thirdsensors and comparing the magnitude or the phase of the spectralcomponents of the first sensor to the magnitude or the phase of thespectral components of the third sensor and the magnitude or the phaseof the spectral components of the second sensor to the magnitude or thephase of the spectral components of the third sensor and combining thosecompared values. The processing subsystem may be configured to adjustthe value of the component phases according to differences in magnitudesof associated spectral components. The processing subsystem may beconfigured to determine the intracranial pressure by combining signalsfrom the first sensor with the signals from the second sensor andcombining the result with signals from the third sensor. The system mayfurther include a display coupled to the processing subsystem configuredto display the intracranial pressure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 shows a depiction of a vasculature of the human head;

FIG. 2 is a three-dimensional view showing the primary components of oneembodiment of the non-invasive intracranial pressure monitoring systemand method thereof of this invention;

FIG. 3 is a photograph showing an enlarged view of the processingsubsystem and the third sensor shown in FIG. 2;

FIG. 4 is flow chart showing the primary steps of one embodiment of themethod for non-invasively determining the intracranial pressuremonitoring system of this invention;

FIG. 5 is flow chart showing in further detail the steps of method fornon-invasively determining the intracranial pressure monitoring systemshown in FIG. 4;

FIG. 6 is flow chart showing the primary steps of another embodiment ofthe method for non-invasively determining the intracranial pressuremonitoring of this invention;

FIG. 7 is flow chart showing the primary steps of yet another embodimentof the method for non-invasively determining the intracranial pressuremonitoring system of this invention;

FIG. 8 is a schematic block diagram overview showing the primarycomponents used by the method for non-invasively determining theintracranial pressure shown in FIGS. 4-6;

FIG. 9 is a schematic block diagram overview showing the primarycomponents used by the method for non-invasively determining theintracranial pressure shown in one or more of FIG. 7;

FIG. 10 is a graph showing exemplary test results of the non-invasiveintracranial pressure system and method shown in one or more of FIGS.2-9;

FIG. 11 shows graphs showing exemplary test results of the non-invasiveintracranial pressure system and method shown in one or more of FIGS.2-9; and

FIG. 12 is a graph showing exemplary test results of the non-invasiveintracranial pressure system and method shown in one or more of FIGS.2-9.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

FIG. 1 shows an example of the vasculature of the human head. One keyvasculature often used in determining ICP is supraorbital artery 10.Supraorbital artery 10 is an example of an artery which receives a flowof blood which emanates from within cranial cavity 14. As can be seen,supraorbital artery 10 is proximate forehead 16 of the skull. Externalcarotid artery 18 is another artery often used to determine ICP.External carotid artery 18 is branched as shown and is an example of anartery which does not receive blood which emanates from cranial cavity14. External carotid artery 18 is located proximate to ear 19 or temple21.

Non-invasive intracranial pressure monitoring system 20, FIG. 2, of oneembodiment of this invention, includes first sensor 22 placed proximatea diffusion field of an artery receiving blood which emanates fromwithin cranial cavity 14, FIG. 1, and is configured to monitorpulsations of that artery. In one example, the diffusion field is acapillary bed and the artery receiving blood which emanates from thecranial cavity is supraorbital artery 10. In this example, sensor 22,FIG. 2, is placed proximate forehead 31 as shown, which is nearsupraorbital artery 10, FIG. 1, as discussed above.

Non-invasive intracranial pressure monitoring system 20, FIG. 2, alsoincludes second sensor 24 placed proximate a perfusion field of anartery which does not receive blood emanating from cranial cavity 14 andis configured to monitor pulsations that artery. Second sensor 24 isplaced approximately the same distance from the heart (not shown) asfirst sensor 22. In this example, the diffusion field is a capillary bedand the artery receiving blood which does not emanate from the cranialcavity is external carotid artery 18, FIG. 1. In this example, sensor 24is placed proximate ear 25 as shown, e.g., on the ear lobe, which isnear external carotid artery 18. In other examples, second sensor 24 maybe placed on or near the temple 21.

Non-invasive intracranial pressure monitoring system also includes thirdsensor 26 placed distally from the heart configured to monitorpulsations of a distal artery. For example, third sensor 26 may beplaced on finger 28 which is located near one or more distal arteriesinside finger 28. In other examples, third sensor may be placed on thehand 32, forearm 34, or any other desired distal location.

Non-invasive intracranial pressure monitoring system 20 also includesprocessing subsystem 30 responsive to signals from first sensor 22,second sensor 24, and third sensor 26 that include data on the monitoredpulsations of the artery receiving blood which emanates from the cranialcavity, the artery receiving blood which does not emanate from thecranial cavity, and the distal artery, respectively to determine theinner cranial pressure.

FIG. 3 shows an enlarged view of processor subsystem 30 and enlargedview of third sensor 26 coupled to processing subsystem 30. Preferably,first sensor 22, FIG. 2, second sensor 24 and/or third sensor 26 arenear infrared (NIR) type sensors. System 20 also preferably includesmonitor 38, FIG. 3, e.g., small LCD screen 33 configured to display andprovide real-time feedback of the determined intracranial pressurevalues.

Non-invasive intracranial pressure monitoring system 20 preferably usesfirst sensor 22, second sensor 24, and third sensor 26 to extract theinformation needed from the perfusion field of the supraorbital artery,the external carotid artery, a distal artery, and other vasculature. Thedata from the supraorbital artery provided by first sensor 22 may beanalyzed with data obtained from an identical second sensor 24 on aperfusion field of the external carotid artery, either on the ear lobe(auricular artery) of ear 25 or on temple 21 (temporal artery). Theselocations are at a comparable distance from the heart as supraorbitalartery 10. Therefore, the external carotid signal from second sensor 24can be used to exclude the part of the signal that stems from whole bodyvascular resistance and pressure. Non-invasive intracranial pressuremonitoring system 20, FIG. 2, also utilizes third sensor 26 placed onthe finger or other part of the body as a reference for signals fromfirst sensor 22 and second sensor 24.

The result is non-invasive intracranial pressure monitoring system 20that non-invasively, accurately, efficiently, effectively, andcontinuously determines ICP. System 20 is small, robust, light weightand utilizes very little power. In one example, system 20 may be able torun for a full day using 4 AA batteries. Thus, system 20 is portable andcan be used in the battlefield, in the field for sports relatedinjuries, or any similar type situation, to provide an accurate measureof ICP to determine the extent of brain injury and enable medical careto timely provide the needed care.

The algorithm for non-invasive intracranial pressure monitoring system20 and methods thereof discussed below are preferably based on relativetime lags between the supraorbital artery and the external carotidartery. First sensor 22, second sensor 24, and third sensor 26,preferably NIR sensors, provide signals, based on the strength of thereflectance of the subtended tissue at the NIR frequency range thatincreases when a pulse passes through the monitored perfusion bed.Recording this signal optically, using NIR sensors, proves to be morerobust and less sensitive to sensor placement or motion artifact thantonometry-based systems.

Non-invasive intracranial pressure monitoring system 20 preferablyoperates on the principle that a less compliant vascular tree propagatesa pressure wave faster than a more compliant tree. Increased pressuresurrounding the vessels, such as the pressure in the cranium surroundingthe internal carotid effectively stiffens the vasculature. Therefore, apressure wave in the internal carotid will traverse the cranial vaultfaster than the same wave traveling in the external carotid. Thedifference between the two may be very small, and in accordance withsystem 20, is preferably more robust to compare each to a distal signalprovided by third sensor 26, e.g., located on the finger, and thencompare the two differences.

In one embodiment, processing subsystem 30 is configured to determinethe intracranial pressure by determining the magnitude and phase of thespectral components of signals from each of first sensor 22, secondsensor 24, and third sensor 26, by comparing the magnitude or the phaseof the spectral components of first sensor 22 to the magnitude or thephase of the spectral components of third sensor 26 and the phase of thespectral components of second sensor 24 to the magnitude or the phase ofthe spectral components of third sensor 26 and combining the comparedvalues. In one example, processing subsystem 30 is configured to adjustthe value of the component phases according to differences in themagnitudes of the associated spectral components. See FIG. 8 (discussedbelow).

In another embodiment, processing subsystem 30 is configured todetermine the intracranial pressure by correlating signals from firstsensor 22 to signals from third sensor 26 and correlating signals fromsecond sensor 24 to third sensor 26 and combining the determinedcorrelations. See FIG. 8 (discussed below).

In yet another embodiment, processing subsystem 30 is configured todetermine the intracranial pressure by combining signals from firstsensor 22 with signals from second sensor 24 and combining that resultwith signals from third sensor 26. See FIG. 9 discussed below.

FIG. 4 shows a flowchart of one embodiment of the method of determiningintracranial pressure using non-invasive intracranial pressuremonitoring system 20, FIG. 2, in accordance with one embodiment of thisinvention. In this example, pulsations of the supraorbital artery 10,FIG. 1, are monitored by first sensor 22, FIG. 2 placed on forehead 31,pulsations of external carotid artery monitored by second sensor 24placed proximate ear 25, and a pulsation of distal artery are monitoredby third sensor 26 placed proximate finger 28, step 50. Signals fromfirst sensor 22 to the third sensor 26 are correlated, step 52. Signalsfrom second sensor 24 and the third sensor are then correlated, step 54.The signals from steps 52 and 54 are combined mathematically todetermine ICP, step 56. See FIG. 8. Flow chart 58, FIG. 5 shows a moredetailed specific implementation of the method shown in FIG. 4.

FIG. 6 shows a flowchart of another embodiment of the method ofdetermining intracranial pressure using non-invasive intracranialpressure monitoring system 20, FIG. 2, in accordance with anotherembodiment of this invention. In this example, pulsations of thesupraorbital artery 10, FIG. 1, are monitored by first sensor 22, FIG.2, placed on forehead 31, pulsations of external carotid artery 18 aremonitored by second sensor 24 placed proximate ear 25, and a pulsationof the distal artery are monitored by third sensor 26 placed proximatefinger 28, step 80. Processing subsystem 30, FIG. 2, responsive to thesignals from first sensor 22, second sensor 24, and third sensor 26,performs a Fourier transform to determine the magnitude and phase ofspectral components of signals output from each of first sensor 22,second sensor 24, and third sensor 26, step 82. The phase of thespectral components of first sensor 22 is compared to the phase of thespectral components of third sensor 26 and the phase of the spectralcomponents of second sensor 24 is compared to the phase of the spectralcomponents of third sensor 26, and the values are combined to determineICP, step 84, FIG. 6. See FIG. 8. Preferably, processing subsystem 30,FIG. 3, is configured to adjust the value of the component phasesaccording to differences in magnitudes of associated spectralcomponents.

FIG. 7 shows a flowchart of another embodiment of the method ofdetermining intracranial pressure using non-invasive intracranialpressure monitoring system 20, FIG. 2, in accordance with anotherembodiment of this invention. In this example, pulsations of thesupraorbital artery 10, FIG. 1, are monitored by first sensor 22, FIG.2, placed on forehead 31, pulsations of external carotid artery 18 aremonitored by second sensor 24 placed proximate ear 25, and a pulsationof distal artery are monitored by third sensor 26 placed proximatefinger 28, step 90, FIG. 7. Processing subsystem 28 is configured todetermine the intracranial pressure by combining signals that aremathematically equal in at least one mathematical measure, such asoffset value or maximum value from first sensor 22 with signals fromsecond sensor 24, step 92. The result of step 92 is combined with signalfrom third sensor 26, step 96. See FIG. 9.

FIG. 8 shows a schematic block diagram overview of the primary stepsassociated with the method of determining intracranial pressure usingnon-invasive intracranial pressure monitoring system 20, FIG. 2, shownin FIGS. 4-6. FIG. 9 shows a schematic block diagram overview of theprimary steps associated with method of determining intracranialpressure using non-invasive intracranial pressure monitoring system 20,FIG. 2, shown in FIG. 7.

An initial demonstration of the non-invasive intracranial pressuremonitoring system 20 and method thereof was conducted in an animal test.This test was used to verify that the ovine model was appropriate forthe test and that non-invasive intracranial pressure monitoring system20 can obtain the necessary data for calculating a measure of ICP. Thisearly prototype utilized a laptop computer to acquire data from thefirst sensor 22, second sensor 24, and third sensor 26. The promisingresults are shown in FIG. 10.

With the preliminary ovine model completed, non-invasive intracranialpressure monitoring system 20 was further tested. The intracranialpressure of a subject was artificially increased due to hydrostaticpressure present in tilt from horizontal to upside down. FIG. 11 showstwo such results from different subjects. Curve 100 indicates the tiltof the chair, from horizontal (zero) to upside down (recorded as 30).The value of 30 was assigned to the chair tilt as it is approximatelythe expected increase in the ICP, in cmH20, due to hydrostatic pressure.In the pilot study on healthy subjects, the exact value of the increasein ICP is unknown, and so the ICP algorithm was scaled by this value of30 cm H20 across the data from all 6 subjects. In the second image shownin FIG. 11 (on the right), the inversion chair did not home properly andunderwent a second, more rapid, inversion. Non-invasive intracranialpressure monitoring system 20 was able to determine the resultantincrease in ICP in both excursions with high fidelity as seen in theimage.

In a separate experiment, non-invasive intracranial pressure monitoringsystem 20 was used to record data during a squat-to-stand test (2minutes of squat to straight standing). Non-invasive intracranialpressure monitoring system and the methods thereof discussed above withreference to one or more of FIGS. 2-9 was able to determine the negativevalue of ICP that is expected with such a test. The results are shown inFIG. 12.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicantcannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is:
 1. A non-invasive intracranial pressure monitoringsystem comprising: a first sensor adapted to be placed proximate to aperfusion field of an artery receiving blood which emanates from thecranial cavity configured to monitor pulsations of the artery receivingblood which emanates from the cranial cavity artery; a second sensoradapted to be placed proximate to a perfusion field of an artery whichdoes not receive blood emanating from the cranial cavity and placedapproximately the same distance from the heart as the first sensorconfigured to monitor pulsations of the artery which does not receiveblood emanating from the cranial cavity; a third sensor adapted to beplaced distally from the heart configured to monitor pulsations of adistal artery; and a processing subsystem responsive to signals from thefirst, second, and third sensors configured to determine an indicationof intracranial pressure by subtracting the first sensor signal from thesecond sensor signal to produce a resultant signal, wherein the firstsensor signal and the second sensor signal are mathematically equal inat least one mathematical measure, and comparing the resultant signal tothe third sensor signal.
 2. The system of claim 1 in which the firstsensor is adapted to be placed on a forehead.
 3. The system of claim 1in which the second sensor is adapted to be placed on a temple.
 4. Thesystem of claim 1 in which the second sensor is adapted to be placed onan ear.
 5. The system of claim 1 in which the third sensor is adapted tobe placed distally on a finger.
 6. The system of claim 1 in which thethird sensor is adapted to be placed distally on a hand.
 7. The systemof claim 1 in which the third sensor is adapted to be placed distally ona forearm.
 8. A non-invasive intracranial pressure monitoring systemcomprising: a first sensor adapted to be placed proximate to asupraorbital artery configured to monitor pulsations of the supraorbitalartery; a second sensor adapted to be placed proximate to a branch of anexternal carotid artery and placed approximately the same distance fromthe heart as the first sensor configured to monitor pulsations of theexternal carotid artery; a third sensor adapted to be placed distallyfrom the heart configured to monitor pulsations of a distal artery; anda processing subsystem responsive to signals from the first, second, andthird sensors configured to determine an indication of intracranialpressure by subtracting the first sensor signal from the second sensorsignal to produce a resultant signal, wherein the first sensor signaland the second sensor signal are mathematically equal in at least onemathematical measure, and comparing the resultant signal to the thirdsensor signal.
 9. The system of claim 8 in which the first sensor isadapted to be placed on a forehead.
 10. The system of claim 8 in whichthe second sensor is adapted to be placed on a temple.
 11. The system ofclaim 8 in which the second sensor is adapted to be placed on an ear.12. The system of claim 8 in which the third sensor is adapted to beplaced distally on a finger.
 13. The system of claim 8 in which thethird sensor is adapted to be placed distally on a hand.
 14. The systemof claim 8 in which the third sensor is adapted to be placed distally ona forearm.
 15. A method for non-invasively determining intracranialpressure, the method comprising: monitoring pulsations of an arteryreceiving blood which emanates from the cranial cavity and generatingfirst output signals; monitoring pulsations of an artery which does notreceive blood emanating from the cranial artery and generating secondoutput signals; monitoring pulsations of a distal artery and generatingthird output signals; and in response to the first, second and thirdoutput signals, determining an indication of the intracranial pressureby subtracting the first sensor signal from the second sensor signal toproduce a resultant signal, wherein the first sensor signal and thesecond sensor signal are mathematically equal in at least onemathematical measure, and comparing the resultant signal to the thirdsensor signal.
 16. The method of claim 15 in which said monitoringpulsations of blood which emanates from the cranial artery is performedproximate a forehead.
 17. The method of claim 15 in which saidmonitoring pulsations of blood which does not emanate from a cranialartery is performed on a temple.
 18. The method of claim 15 in whichsaid monitoring pulsations of blood which does not emanate from acranial artery is performed on an ear.
 19. The method of claim 15 inwhich said monitoring pulsations of the distal artery is performed on afinger.
 20. The method of claim 15 in which said monitoring pulsationsof the distal artery is performed on a hand.
 21. The method of claim 15in which said monitoring pulsations of the distal artery is performed ona forearm.
 22. A non-invasive method for determining intracranialpressure, the method comprising: monitoring pulsations of a supraorbitalartery and generating first output signals; monitoring pulsations of anexternal carotid artery and generating second output signals; monitoringpulsations of a distal artery and generating third output signals; andin response to the first, second, and third output signals determiningan indication of the intracranial pressure by subtracting the firstsensor signal from the second sensor signal to produce a resultantsignal, wherein the first sensor signal and the second sensor signal aremathematically equal in at least one mathematical measure, and comparingthe resultant signal to the third sensor signal.
 23. The method of claim22 in which said monitoring pulsations of the supraorbital artery isperformed on a forehead.
 24. The method of claim 22 in which monitoringpulsations of the external carotid artery is performed on a temple. 25.The method of claim 22 in which monitoring pulsations of the externalcarotid artery is performed on an ear.
 26. The method of claim 22 inwhich monitoring pulsations of the distal artery is performed on afinger.
 27. The method of claim 22 in which monitoring pulsations of thedistal artery is performed on a hand.
 28. The method of claim 22 inwhich monitoring pulsations of the distal artery is performed on aforearm.